1. Field of the Invention
The present invention relates to an optical detector device that extracts moving objects in incident optical images.
2. Related Background Art
Optical detector devices fabricated by CMOS technologies can be built for a low cost on a single chip that includes the A/D converter circuits and the peripheral digital circuitry. Because of this, optical detector devices have been developed that, rather than just detecting light, include a variety of processing functions (for example, outline extraction or moving object extraction) on a single chip.
An optical detector device that has a moving object extraction function is described, for example, in Ishiwata, et al., xe2x80x9cCMOS lmage Sensor for the Recognition of Three-Dimensional Gestures,xe2x80x9d Image Information Media Association Technical Reports, Vol. 23, No. 30, pgs 13-16 (1999).
The optical detector device described in this reference is equipped with two capacitors and plurality of switches for each pixel, where the image data is stored in the first capacitors when one frame is captured and the image data is stored in the second capacitors when the next frame is captured, following which the differences between the image data stored in the respective first and second capacitors are derived.
By the above, the optical detector device extracts moving objects by performing image processing on the chip. This optical detector device provides separate image memory, whereas, conventionally, the image processing has had to be performed after storing the image data in an image memory provided separately.
In the optical detector device having a moving object extraction function, described in the aforementioned reference, it has been necessary to provide two capacitors and plurality of switches for each pixel, and also necessary to provide a differential circuit for finding the differences between the image data stored, respectively, in the first and second capacitors. Consequently, the area required on the chip for the circuitry for each pixel in this optical detector device has been large, and, as a result, this optical detector device has had the fatal flaw that it could not achieve a high aperture ratio, which determines the light response characteristics of the sensor, and thus could not provide images with high image quality.
The present invention was created to solve the aforementioned problem area, and is an optical detector device that extracts moving objects in the incident image with the object of reducing the surface area on the chip required for the circuitry for each pixel, thereby providing a high aperture ratio and superior optical response characteristics.
The optical detector device of the present invention comprises (A) an optical detector part that has an optical detector element that generate charges according to the intensity of incident light and a capacitor with a specific capacitance and that accumulates the charge generated by the aforementioned optical detector element, (B) an integrator circuit connected to the aforementioned capacitor, and having an integrated circuit capacitor with the aforementioned specific capacitance disposed between the input and output terminals of an amplifier, (C) a first switch equipped between the input terminal of said integrator circuit and the aforementioned optical detector part, and (D) a second switch equipped between the output terminal of the aforementioned integrator circuit and the aforementioned optical detector part. This will be explained in detail below.
A first optical detector device comprises (1) an optical detector part that is equipped with an optical detector element that generates a charge depending on the intensity of incident light and a capacitor that has a capacitance Cd and that accumulates the charge generated by the optical detector element; (2) an integrator circuit which has an amplifier and an integrator circuit capacitor with a capacitance of Cf1 (where Cd=Cf1), disposed in parallel between the input terminal and the output terminal thereof, which accumulates the charge that is inputted into the input terminal in the integrator circuit capacitor, and outputs from its output terminal an integrated output according to the amount of the charge accumulated; (3) a first switch equipped between the optical detector part and the input terminal of the integrator circuit; and (4) a second switch equipped between the integrator circuit output terminal and the optical detector part.
In this first optical detector device, the charge that is generated according to the intensity of light that is incident upon an optical detector element in the optical detector device during a given time interval is stored in the capacitor. If the first switched is closed at the point in time this given time interval elapses, the charge that has been stored thus far in the capacitor moves to the integrator circuit capacitor in the integrator circuit.
The result is that the voltage at one terminal of the optical detector element changes by xcex94V to assume the reset level, and the integrator output, which is outputted from the integrator circuit, assumes a level according to the charge that was accumulated in the integrator circuit capacitor. When the second switch closes after the first switch has been opened, a voltage determined by the value of the integrator output, outputted from the integrator circuit, is placed into the capacitor in the optical detector element. Because the capacitance of the integrator circuit capacitor is the same as the capacitance of the capacitor in the optical detector element, the result is that the voltage at the terminal on one side of the optical detector element changes from the reset level by an amount equal to xcex94V.
For a specific time interval thereafter, the amount of charge that is generated, which depends on the intensity of light that is incident on the optical detector element, is stored in the capacitor. At the point in time this specific time interval elapses, the charge that has been accumulated in the capacitor is the superposition of the charge that is proportional to the voltage that was set according to the value of the integrator output when the second switch was closed, along with the charge that was generated in the optical detector element over the specific time interval. However, because the charges that are superposed have mutually differing signs, when the first switch is closed when this specific time interval elapses, the output of the integrator circuit is dependent on the increase or decrease of the intensity of light that is incident on the optical detector element.
A second optical detector device is equipped with (1) an optical detector part that has an optical detector element that generates charges according to the intensity of incident light, and a capacitor with a capacitance Cd, and that accumulates the charges that are generated by the optical detector element; (2) an integrator circuit which has an amplifier and a integrator circuit capacitor equipped in parallel between the input terminal and the output terminal thereof, and which further comprises a capacitance switching means that is able to switch the capacitance of the integrator circuit capacitor between a capacitance Cd and a smaller value, and which accumulates the charge that is inputted into the input terminal in the integrator circuit capacitor and outputs the integrator output, which is dependent on the amount of charge accumulated, from the output terminal; (3) a first switch that is equipped between the optical detector part and the input terminal of the integrator circuit; and (4) a second switch that is equipped between the output terminal of the integrator circuit and the optical detector part.
In this second optical detector device, the charges that are generated depending on the intensity of light that is incident on the optical detector elements of the optical detector part over a specific time interval are accumulated in the capacitors. When a first switch closes as the specific time interval elapses, the charge that has accumulated in the capacitor up until that point moves to the integrator circuit capacitor in the integrator circuit.
As a result, the voltage on one of the terminals of the optical detector element changes by xcex94V to assume the reset level, and the integrator output, which is outputted from the integrator circuit, goes to a level that is dependant on the charge that has been accumulated in the integrator circuit capacitor. When the second switch is closed after the first switch has been opened, a voltage, which is dependant on the value of the integrator output that is outputted from the integrator circuit, is set into the capacitor in the optical detector element. At this time, the capacitance switching means has caused the capacitance of the integrator circuit capacitor to be the same as the capacitance of the capacitor in the optical detector element, with the result that the voltage at the one terminal of the optical detector element changes from the reset level by an amount of xcex94V.
After this point, the charge that is generated during the specific time interval according to the intensity of light that is incident on the optical detector element is accumulated in the capacitor. After this specific amount of time has elapsed, the charge that has been accumulated in the capacitor is the superposition of the charge that is proportional to the voltage that was set according to the value of the integrator output at the time that the second switch was closed, and the charge that was generated in the optical detector element over the specific time interval.
However, the signs of the charge accumulated are mutually differing. At this point, the capacitance switching means causes the capacitance of the integrator circuit capacitor to assume a value that is smaller than the capacitance of the capacitor in the optical element. Consequently, when the first switch is closed as this time interval elapses, the integration output, which is outputted from the integrator circuit, depends on whether the intensity of incident light on the detector element increased or decreased, and the change in the intensity of light is detected with excellent sensitivity.
In addition, the first and second optical detector devices according to the present invention are also provided with an optical change range detection circuit that detects whether or not the integrator output (voltage) is within a specific range. In this case, the optical change can be obtained as binary data, simplifying the processing from this point forward.
Furthermore, the first and second optical detector devices according to the present invention are further equipped with a CDS (Correlated Double Sampling) circuit, which outputs a CDS output value according to the amount of change in the integrator output value. This eliminates the influence of any offset variation that is included in the integrator output that is outputted from the integrator circuit. In addition to this, preferably an optical change range detector circuit, which detects whether or not the CDS output value is within a specific range, is also provided.
The first and second optical detector devices according to the present invention further comprises a single set consisting of an integrator circuit and first and second switches for all of the plurality of optical detector parts, and the plurality of optical detector parts are connected sequentially to the integrator circuit. Conversely, a single set of an integrator circuit, a first switch, a second switch, and an optical change range detector circuit is equipped for all of the plurality of optical detector parts, and each of the plurality of optical detector parts is connected sequentially to the integrator circuit.
Alternatively, a single set consisting of an integrator circuit, a first switch, a second switch, and a CDS circuit is equipped for all of the plurality of optical detector parts, and the plurality of detector parts are connected sequentially to the integrator circuit. Alternatively, a single set consisting of an integrator circuit, a first switch, a second switch, a CDS circuit and an optical change range detector circuit is equipped for all of the plurality of optical detector parts, and the plurality of optical detector parts are connected sequentially to the integrator circuit.
In each of these cases, the optical detector device can detect increases and decreases in the light intensity for each individual pixel in the image, and is thus able to extract moving objects. The scope of the circuit required for each pixel in this optical detector device is substantially smaller than in conventional technologies. In particular, when the junction capacitance of the optical detector element is used as the capacitor, the size of the circuit is even smaller. Consequently, in this optical detector device, the surface area on the chip required for the circuit part for each pixel is small, so the aperture ratio for each pixel is large, producing superior optical response characteristics.